I have a sample of liquid CO2 which should be analysed for benzene at ppb level. It's pretty unusual kind of analysis for our lab. Would it be possible to recommend me the right method, or source where I can find apptopriate method?

We have couple of Varians with various detectors and columns.

Thanks

You might try putting some of the liquid CO2 into a sample container (such as a Tedlar bag) and allowing it to vaporize. Obviously, you will have to account for the large expansion volume of the resulting vapor. Then do some large volume (1 mL or greater) direct injections of the gas into the GC. You may need to cool the oven or injector using cryogenics down to a low temperature to refocus the benzene sample band. I would use a PID or MSD (possibly in SIM mode).

You may also be able to do an actual liquid injection using a gas/liquid sampling valve designed for this purpose. There are valves out there that are used for injection of LPG and liquefied gases. I'd contact Valco Instruments (they make valves) for more information on this solution. However, I'm a little skeptical about the final sensitivity that you will be able to achieve using this method due to the very small sample size you will have to inject (much less than 1 uL).

Good luck!
Jason Ellis
Applications Chemist
J&W Scientific, Inc.
e-mail: jasone@jandw.com

Personally, I like the idea of injecting CO2 as a liquid. Valco makes a 4-port liquid inject valve that will work nicely at the approximately 1000 psig you will have for liquid CO2. Mount the valve outside in the oven, inject at a low temperature, and gently raise the temperature to elute Benzene. You can easily calculate what 1 microliter of LCO2 will expand to when it vaporizes. Almost any column will separate Benzene from CO2.

Got a PID instead of an FID? Nice for Benzene.

Got a purge & trap around? Rig it to sample the vaporized CO2, and the concentration effect in the standard P&T columns will be excellent for ultra-trace Benzene. Obviously, when you try to vaporize CO2, you will need to heat-trace the downstream tubing to prevent condensation of trace Benzene in cold tubing, but at your concentration, excessive heating is not required. Room temperature will suffice.

Good Luck!

Bill Jenko
Sr. Chemist
Seimens Applied Automation